1. Field of the Invention
This invention relates to a method of manufacturing a gradient magnetic field coil assembly of an MRI apparatus.
2. Description of the Related Art
With an MRI apparatus, the gradient fields generated by Gx, Gy and Gz gradient magnetic field coils are superposed on static magnetic fields. The combination of the Gx, Gy and Gz gradient magnetic fields specifies a slice position of an object to be examined at which a tomographic image is obtained.
Each of the Gx and Gy gradient magnetic field coils comprises a plurality of saddle coils and the Gz gradient magnetic field coil comprises a solenoid coil. The accuracy of the slice position is much influenced by the positional accuracies of the saddle coils and the solenoid coil.
The conventional saddle coils are embedded in a molded resin member having a curved surface. The saddle coil assembly is manufactured as follows:
Wires which will form saddle coils are temporarily positioned on the flat surface of a metal mold by means of pins at predetermined positions. Molten resin is poured on the flat surface and cured. Thus, a flat molded resin member embedded with saddle coils is formed. The member is removed from the metal mold and is bent so as to have a predetermined curved surface. A plurality of molded resin members embedded with a plurality of saddle coils and a solenoid coil manufactured separately from the saddle coils is provided in a cylindrical molded resin body so that Gx, Gy and Gz gradient magnetic fields are produced.
However, the saddle coils are placed in the predetermined positions only by the pins, lowering the positional accuracies of the wires. This lowers the positional accuracies of the formed saddle coils, resulting in a low detecting accuracy of the slice position.
Although the wires are positioned by the pins along the flat mold surface, they are not positioned by the pins perpendicularly thereto. As a result, the wires wave on planes perpendicular to the flat mold surface, greatly lowering the perpendicular positional accuracies of the wires.
Since the molded resin members embedded with the saddle coils is bent after it has been formed flat, the positional accuracies of the saddle coils are not so good. Further, the higher the rigidity of the wires becomes, the lower the positional accuracies of the wires become.